Compound control system for a turbine



Sept. 13, 1966 R. L. CARSON COMPOUND CONTROL SYSTEM FOR A TURBINE Filed May 24, 1965 HIS ATTORNEY.

United States Patent Oiiice 3,2 71,953 Patented Sept. 13, 1966 3,271,953 COMPUND CONTROL SYSTEM FR A TURBINE Robert L. Carson, Scotia, N.Y., assigner to General lElectric Company, a corporation of New York Filed May Z4, 1965, Ser. No. 453,334 Claims. (Cl. 611-43) This invention relates generally to a control system for a turbine and in particular to an improved compound control system wherein turbine speed and motive fluid pressure act interdependently to control the speed and pressure in a turbine generator plant.

While the practice of this invention is subject to a wide variety of modifications and variations, it is suited for use with a dual cycle boiling water type nuclear reactor plant for supplying steam to a turbine and is so described herein.

In a boiling Water reactor plant, water cools the reactor and in doing so, is partially converted to steam which is caused to How directly from the reactor to a turbine. In a dual-cycle boiling water reactor plant, the coolant is not only used as a direct source of steam, but a portion of it is passed to a heat exchanger or steam generator to provide a secondary source of steam. This steam is necessarily of a lower pressure and is introduced at intermediate or low pressure stages of the turbine system. In addition to the primary steam to the high pressure side of the turbine, and the secondary steam to the intermediate or low pressure side, there is a steam bypass which dumps primary steam directly to the condenser in the event of excessive pressure. Hence there are three sets of valves to position and regulate: primary control valves which admit high pressure reactor steam to the turbine; secondary control valves which admit steam from the secondary steam generator to the turbine; bypass valves which bypass the turbine and put reactor steam directly into the condenser if more primary steam -is 4being produced than is being taken by the turbine.

Patent No. 3,022,235 issued Feb. 20, 1962, to Dale H. Brown and David W. Leiby and assigned to the assignee of the present application, discloses a regulating system of the general type herein disclosed by which the sets of valves are properly coordinated by the interdependent action of a speed responsive and a pressure responsive governing means.

The present invention provides a regulating system of the same general type as above mentioned. However, in addition to this structure, the present invention provides a hydraulic system which is responsive to the signals of the two interdependent governors, and by which those signals are amplified to produce the motions called for. That is to say that, since the signals of the present system are hydraulically amplified to perform the function of opening and closing certain valves, the apparatus and structure by which the signals are sensed and relayed can be smaller than the equivalent apparatus in a system which has no hydraulic amplification.

Accordingly, it is an object of the present invention to provide an improved compound control system for a turbine which operates at comparatively low force levels.

Another object of this invention is to provide an improved compound control system for a turbine which reduces friction and hysteresis, thus providing improved regulation.

These and other objects, features, and advantages of this invention will be readily appreciated from the following description when considered in connection with the accompanying drawing, which is a schematic diagram of the control system of this invention, and shown in working relation to a nuclear powered steam turbine system which is in a state of equilibrium.

Briefly stated, in accordance with one of its aspects, this invention comprises a `turbine control system including a primary or high pressure steam valve, a secondary or lower pressure steam valve, ya turbine bypass steam valve, a speed governor regulating the secondary valve, a pressure responsive governor regulating the bypass valve, and the speed governor and pressure responsive governor acting together to regulate the primary valve.

Referring now to the drawing, a boiling water nuclear reactor 1 provides steam for turbine 2 directly through a primary steam line 3 and indirectly by way of secondary steam line 4 from steam generator 5 which is a heat exchanger taking heat from reactor coolant loop 6 and giving it up to the steam in secondary steam line 4. A steam bypass Aline 7 connects primary steam line 3 directly to the shell side of condenser 8, allowing steam to bypass the turbine and exhaust directly to the condenser in certain conditions of low turbine load or turbine overspeed. The primary steam line 3, secondary steam line 4 and bypass steam line 7 are controlled by throttle Valves 9, 10 and 11 respectively, which are in turn actuated by servo motors 12, 13 and 14 respectively. A centrifugal governor 15 is driven Iby and controls the speed of lturbine 2. A pressure sensitive governor or pressure regulator 16 is responsive to and controls the pressure of primary steam in line 3.

Speed governor 15 acts to regulate the speed or load on the turbine by way of a control mechanism which includes an arm 2t) Iwhich is pivotally connected at one end 21 to an arm 15a and at the other end 22 to the end of another arm 24. Arm 15a is actuated by the speed governor 15 yon one end and its fulcrum at `the other end is adjusted by load reference selector 15b. At a point 23 intermediate its ends 21 and 22, arm 20 is pivotally connected to the spindle of a speed control pilot valve 40 which is in turn directly connected to the input signal of secondary valve servomotor 13.

Pressure sensitive governor or pressure regulator 16 acts to regulate the pressure of primary steam by way of a control mechanism, similar to that connected to the speed governor, which includes an arm 30 which is pivotally connected at one end 31 to the pressure regulator 16 and at the other end 32 to the end of another arm 34. At a point 33 intermediate its -ends 31 and 32, arm 30 is pivotally connected to the spindle of a pressure control pilot valve 50 which is in turn directly connected to the input lsignal of bypass valve servornotor 14.

Arms 24 and 34 are pivotally connected to fixed structures at points 25 and 35 intermediate their ends. End points 26 and 36 of arms 24 and 34 respectively are pivotally connected to the spindle of a single acting cylinder or primary relay 60 which is in turn directly connected to the input signal of primary valve servomotor 12. Therefore arms 24 and 34 act as restoring linkages for pilot valves 40 and 50 respectively.

Primary relay 60 includes a piston 61 which is biased in one direction by a spring 62 and in the other .by hydraulic pressure. Hydraulic pressure `to primary relay 60 is supplied through the aforementioned pilot valves 40 and 50, these being connected in series as follows. Speed control pilot valve 40 and pressure control pilot valve 50 each have three ports. Pressure port 51 of valve 50 is connected to a hydraulic pressure sourc-e (not shown). Exhaust port 52 is vented to an oil reservoir (not shown). Outlet port 53 is connected to pressure port 41 of speed control pilot valve 40. Exhaust port 42 is vented to an oil reservoir (not shown). Outlet port 43 is connected to the hydraulic side of primary relay 60.

Directly connected to the spindles 40a and 50a respectively of each pilot valve 40 and 50 and of the primary relay 60 are indicators which move with their respective spindles relative to stationary indicator scales which read in terms of the degree of opening or closing of steaml throttle -valves 9, and 11. For the purpose of understanding the invention, the secondary steam control valve 10 can be pictured as moving up and down with the pilot valve spindle 40a. Similarly the steam bypass valve 11 can be pictured as moving up and down with pilot valve spindle 50a. Therefore each pilot valve spindle performs a dual function of moving a steam valve directly and also controlling oil ow to the primary relay 60.

The operat-ion of the controlling servomechanism consisting of pilot valves 40, 50, primary relay 60 and associ- `ated linkages will rst be described without reference to the power plant or the steam valves 10 and 11 which are additionally moved by direct action of the pilot valves. Input movements at points 21 or 31 will move pilot valve spindles 40a, 50a respectively. Since pilot valves 40, 50 are connected in series to control oil to a common servomotor piston 61 of primary relay 60, each pilot valve is capable of overriding the other one in a predetermined direction. The connections are such that the pilot valve demanding the lowest position of piston 61 will exercise control. The overridden pilot valve will have its spindle elevated above the controlling position by an amount proportional to the difference between the servomotor position called for by the overridden pilot valve and the servomotor position actually assumed due lto the action of the other (overriding) pilot valve. Thus the overridden pilot valve, though inactive insofar as primary relay 60 is concerned, moves by an amount proportional to a deficiency or error in the servomechanism failing to satisfy two input signals at the same time. This error signal `can 'thereforebe utilized to control additional valves, i.e. steam valves 10 or 11, to satisfy the conflicting requirements of two input signals to the same relay 60 controlling primary steam valve 9.

The operation of the system will now be described. For a reference point, assume an initial or normal operating condition as shown in FIG. 1, wherein primary steam pressure is controlled by the pressure regulator positioning the primary valve 9, and turbine load is maintained by primary steam alone, so that secondary steam throttle valve 10 is closed, bypass steam throttle valve 11 is closed, and primary steam throttle valve 9 is at a point Ibetween fully open and closed. Also, pilot valve spindle 50a is -in a controlling position on port 53 and pilot valve spinde 40a is slightly above port 43, permitting hydraulic uid to communicate from pilot valve 50 to primary relay 60.

Assume now that load on the turbine is increased. This is accomplished either by the operators action in utilizing the load reference selector b to raise the fulcrum of lever 15a with the speed remaining fixed, or by the speed governor 15 raising the left-hand end of lever 15a due to a decrease of turbine speed.

It will be understood Iby those skilled in the art that when the turbine-generator is electrically interconnected with other turbine-generators in a large power system, as is the usual case, so that load is shared by many units, the speed governor 15 is actually sensing speed, i.e. electrical frequency -of the total system. Small variations in speed, therefore, become a measure of the load which is added or shed by turbine 2.

Increase in load, therefore, will cause point 21 on lever to move upward. It will Ibe understood that the foregoing description applicable to a system of interconnected turbine-generators would also be applicable if the unit shown were operating separately and that a decrease in speed, either because of added load or for some other reason, will also cause point 21 to move upward. This action raises spindle 40a of pilot valve 40 increasing the opening of port 43. However, pilot valve 50 is responsive only to regulation by the pressure regulator 16 land since there has been no pressure regulator signal, pilot valve 50 does not move and port 53 remains closed. Therefore, although speed governor 15 wants to increase hydraulic pressure to primary relay 60 to signal servomotor 12 to open primary valve 9, the speed governor is overruled by the pressure regulator. The two must work in concert to open primary valve 9. Neither the pressure regulator nor the speed governor can do it alone. However, to lower or close the primary valve 9, either the pressure regulator or the speed governor, whichever requires a lower valve position, will override the other and is able to control it alone. The lifting of pilot valve 40 above the controlling position at port 43 indicates a failure of primary relay 60 to respond to the signal for a load increase. The distance which pilot valve 40 is lifted above the port position is a measure of the error between the load desired by the speed governor and the load carried by the primary valve. This error signal is used to position the secondary valve. When the pilot valve 40 rises more than a predetermined small amount above the port position, the input to servomotor 13 will cause the secondary valve 10 to start to open. In this manner, any portion of the load demand not satised by the primary valve will be supplied by the secondary valve. The speed governor 15 thus has unrestricted control of turbine power in response to load, regardless of the condition in the pressure control system. The governor will put steam into the turbine through the primary valve 9 preferentially, but if restricted by the pressure control system, it will automatically open the secondary valve 10 to get Whatever power is required to carry whatever Iadditional load is sensed.

Assume now, that the load is returned to normal by the removal of the added load. Governor 15 will pull lever 20 down and with it the spindle of valve 40 which, through its signal to servomotor 13 closes secondary Valve 10. The system is once again at the reference condition of FIG. 1.

Assume that the turbine load is further reduced either by lowering the load reference selector 15b or by governor 15 sensing an increase .in speed. Governor 15 will lower pilot valve 40 until it reaches the controlling position at port 43. Any further lowering of point 21 will cause the speed control pilot valve 40 to lower the primary relay piston 61, by venting through port 42, taking control away from the pressure control pilot valve. Lowering of piston 61 causes point 36 to lower and points 32 and 33 to rise. Point 31 remains fixed because it is positioned only by reactor pressure. When pilot valve 50 rises a small predetermined amount above the controlling position on port 53, the servo motor 14 will begin to open the bypass valve 11. Thus the lifting of pilot valve 50 above the port position, which occurs as a result of pilot valve 40 tak-ing control of the primary relay 60, becomes the error signal which opens the bypass valves. There has been no pressure disturbance and no repositioning of the pressure regulator 16 has been necessary. The lifting of point 33 by levers 30 and 34 has caused the bypass valves to open the amount necessary to maintain constant primary steam flow .from the reactor even though the primary steam ow to the turbine has been reduced.

The pressure control system thus has unrestricted control of reactor steam pressure regardless of the condition in the speed control system. The pressure control system will put steam into the turbine through the primary valve 9 preferentially, but if the primary valve is restricted by the speed governor, the bypass valve 11 will be opened Iautomatically by the amount necessary to maintain the desired reactor pressure.

Assume now that the load is increased back to the original level. Governor 15 pushes point 21 up. The piston 61 will rise under control of pilot valve 40 at port 43. As piston 61 rises, opening the primary valve and increasing primary ow to the turbine, point 36 is raised and points 32 and 33 are lowered. The lowering of point 33 causes lowering lof the servomotor 14 and closing of bypass valve 11. In this manner, the bypass valve is closed by the same amount the primary valve is opened and the flow from the reactor remains constant. When point 33 is lowered to the point where pilot valve 50 is in a controlling position at port 53, the bypass valve will be fully closed. The governor 15 will not be able to open the primary valve further because there is no more primary steam available and pilot valve 50 has overridden pilot valve 40. Any additional load demand from the governor will cause pilot valve 4l) to be lifted above the controlling port 43 and the secondary valve will open to satisfy the load requirement.

In the manner which has been described the speed governor has unrestricted control of turbine load, Within the limitations of the system capacity, by first opening the` primary valve preferentially and then the secondary valve if opening of the primary valve is restricted by other means. The overlifting of pilot valve 40 beyond the controlling port 43 provides the error signal which positions the secondary valve automatically to the position necessary to satisfy the load requirements.

Similarly, the pressure regulator has unrestricted control of the reactor pressure by first opening the primary valve preferentially and then the bypass valve if opening of the primary valve is restricted by other means. The overlifting of pilot valve 50 beyond `the controlling port 53 provides the error signal which positions the bypass valve automatically to the position required by the regulator to maintain the desired reactor pressure.

In a modified form of this invention, where there is no secondary steam system, the speed governor 15 will function as described above, except that valve and servo 13 would be eliminated, i.e. the spindle of speed control pilot valve 40 would not be connected to anything other than arm 20. In this modification, speed governor 15 functions only to oversee primary valve 9 in conjunction with the pressure control system. The pressure regulator would function as described, controlling reactor pressure by opening the primary valve preferentially, and the bypass valve if opening of the primary valve were restricted.

It is apparent that the compound control system of this invention is suited for use with power sources and powerplants other than the illustrated dual cycle boiling Water reactor plant.

The specific embodiment described herein is presented as an example and it will occur to persons of ordinary skill in the art to make modifications Within the invent-ive concept herein disclosed. Accordingly, it is intended that the invention be not limited by the details in which it has been described, but that yit encompass -all within the purview of the following claims:

What is claimed is:

1. A control system for a turbine supplied with motive fluid from a pressure source comprising:

(a) a primary valve connected to control flow of motive fluid from said pressure source to said turbine,

(rb) an .additional valve connected to control motive fluid from said source so as to adjust any unbalance between motive fluid flow generated by the pressure source at a given pressure and motive fluid flow required by the turbine at a given load,

(c) first means responsive to motive fluid pressure including a first pilot valve controlled thereby,

(d) second means responsive to the speed of said turbine including a second pilot valve controlled thereby,

(e) a primary servomotor controlled jointly by said first and second pilot valves and arranged to move said primary valve toward a more open position upon increase in motive fluid pressure or decrease in turbine speed respectively, said pilot valves being connected so that the pilot valve requesting the lowest primary valve position overrides the other pilot valve to eX- ercise sole control over the primary servomotor while the overridden pilot valve moves in an unrestricted manner, whereby the motion of the overridden pilot valve indicates the potential unbalance in motive fluid flow between pressure source and turbine, and

(f) `an additional servomotor connected to actuate said additional valve to correct said unbalance in response to movements of the overridden pilot valve.

2. The combination according to claim 1 where said additional valve is a Valve causing motive fluid to bypass the turbine and where said additional servomotor is connected to be actuated by the first pilot valve.

3. The combination according to claim 1 where said additional valve controls a supplementary source of motive fluid from the pressure source to the turbine and where said additional servomotor is connected to be actuated by the second pilot valve.

4. A control system for a turbine comprising:

(a) a primary valve controlling the flow of primary motive fluid from a pressure source to said turbine,

-(b) a secondary valve controlling the flow of secondary motive fluid from said pressure source to said turbine,

(c) a bypass valve controlling the flow of motive fluid in a line from said pressure source bypassing said turbine,

(d) first means responsive to motive fluid pressure including a first pilot valve controlled thereby,

(e) second means responsive to the speed of said turbine including a second pilot valve controlled there- (f a fluid mot-or operatively connected to said primary valve and controlled jointly by said first and second pilot valves and arranged to move said primary valve toward ya more open position upon increase in motive fluid pressure or decrease in turbine speed respectively, said pilot valves being connected in series so that t-he pilot valve requiring the lowermost primary valve position overrides the other pilot valve to exercise sole control over the fluid motor while the overridden pilot valve moves in an unrestricted manner, whereby the m-otion of the overridden pilot valve indicates the potential unbalance in motive fluid flow between the pressure source and turbine,

(g) said first pilot valve being further operatively connected to said bypass valve, the movement of said first pilot valve controlling the degree of opening of said bypass valve, and

(h) said second pilot valve being further operativelyconnected to said secondary valve, the movement of said second pilot valve controlling t-he degree of opening of said secondary valve.

S. A control system for a turbine comprising:

(a) a primary valve controlling the flow of primary motive fluid from a primary pressure source to said turbine,

(b) a secondary valve controlling the flow of secondary motive fluid from a secondary pressure source to said turbine,

(c) a bypass valve controlling the flow of motive fluid in a line from said primary pressure source bypassing said turbine,

(d) means responsive to the pressure of said motive fluid controlling said bypass valve,

(e) a first pilot valve controlled by said pressure responsive means,

(f) means responsive to the speed of said turbine controlling said secondary valve,

(g) a second pilot valve controlled by said responsive means,

(h) means to open said primary valve `comprising a single-acting lluid cylinder operatively connected thereto, the power stroke of said cylinder causing opening of said primary valve,

(i) said first `and second pilot valves connected in series, said second pilot valve controlling fluid flow to said fluid cylinder, said first pilot valve controlling fluid Vflow to said second pilot valve,

(j) `said first pilot valve being further operatively con- References Cited by the Examiner UNITED STATES PATENTS 1,621,435 3/1927 Rosch 60--43 5 3,022,235 2/1962 Br-OWn et al. 60-43 X 3,029,197 4/ 1962 Untermyer 60-43 EDGAR W. GEOGHEGAN, Primary Examiner. 

1. A CONTROL SYSTEM FOR A TURBINE SUPPLIED WITH MOTIVE FLUID FROM A PRESSURE SOURCE COMPRISING: (A) A PRIMARY VALVE CONNECTED TO CONTROL FLOW OF MOTIVE FLUID FROM SAID PRESSURE SOURCE TO SAID TURBINE, (B) AN ADDITIONAL VALVE CONNECTED TO CONTROL MOTIVE FLUID FROM SAID SOURCE SO AS TO ADJUST ANY UNBALANCE BETWEEN MOTIVE FLUID FLOW GENERATED BY THE PRESSURE SOURCE AT A GIVEN PRESSURE AND MOTIVE FLUID FLOW REQUIRED BY THE TURBINE AT A GIVEN LOAD, (C) FIRST MEANS RESPONSIVE TO MOTVE FLUID PRESSURE INCLUDING A FIRST PILOT VALVE CONTROLLED THEREBY, (D) SECOND MEANS RESPONSIVE TO THE SPEED OF SAID TURBINE INCLUDING A SECOND PILOT VALVE CONTROLLED THEREBY, (E) A PRIMARY SERVOMOTOR CONTROLLED JOINTLY BY SAID FIRST AND SECOND PILOT VALVES AND ARRANGED TO MOVE SAID PRIMARY VALVE TOWARD A MORE OPEN POSITION UPON INCREASE IN MOTIVE FLUID PRESSURE OR DECREASE IN TURBINE SPEED RESPECTIVELY, SAID PIVOT VALVES BEING CONNECTED SO THAT THE PILOT VALVE REQUESTING THE LOWEST PRIMARY VALVE POSITION OVERRIDES THE OTHER PILOT VALVE TO EXERCISE SOLE CONTROL OVER THE PRIMARY SERVOMOTOR WHILE THE OVERRIDDEN PILOT VALVE MOVES IN AN UNRESTRICTED 